1. Field of the Invention
The invention relates in particular to materials crosslinkable at room temperature and based on organosilicon compounds, e.g. so-called RTV-1 materials, and special tin compounds which can be used as a catalyst in these materials.
2. Background Art
The use of dialkyltin(IV) compounds as condensation catalysts in RTV-1 and RTV-2 silicone rubbers is generally known. In RTV-1 alkoxy materials, these tin compounds, however, have the disadvantage that they also catalyze the undesired cleavage of the siloxane chains by alcohol radicals (“equilibration”), terminal alkoxy groups of the polysiloxane chain forming which are no longer crosslinkable and hence sufficient crosslinking of the material no longer being possible; i.e. with use in the intended manner, no vulcanized product or an insufficiently stable vulcanized product is obtained. The shelf life, stated as the duration for which the RTV-1 material can be stored, without markedly losing its properties, is drastically reduced by the equilibration.
The methods of choice for increasing the shelf life are to date                replacement of the tin catalyst by a titanium catalyst. The disadvantage here is the yellow coloration of the materials, with the result that only opaque but not translucent materials are possible.        reduction in the amount of the tin catalyst.        use of less aggressive tin catalysts, for example tin chelate catalysts. An excess of chelate compound, such as, for example acetylacetonate, is necessary; however, this is volatile, toxicologically unsafe and hazardous to health.        addition of alcohol scavengers which, owing to their high reactivity, react with alcohols. This addition is, however, expensive and generally impairs the adhesion behavior.        use of catalysts having Sn—O—P bonds, as described, for example, in EP-A 850 254, which are obtained by reacting phosphoric monoesters with organic tin compounds. However, it has been found that the very high acid number of the phosphorus compounds used, which have to be employed at least in equimolar amounts relative to the tin compound or in an excess, cause adhesion problems which are evident in particular when the adhesive joints are in contact with water. Moreover, compounds having Sn—O—P bonds, obtained from phosphorus diesters, are disclosed in U.S. Pat. No. 3,525,778 and U.S. Pat. No. 3,655,705.        
Dialkyldiacyltin catalysts blocked with sulfonic acid and intended for polyurethanes are known, the activation being effected via amines. In this context, reference may be made, for example, to U.S. Pat. No. 5,849,864 and WO99/11369, Ashland Chemical Company. Organotin-based RTV-2 curing agents (catalyst-crosslinking agent compositions) are described in DE-A 195 27 101 and may also contain organic acids as reaction time regulators, the reaction time regulators being intended to improve the reactivity of the claimed catalyst-crosslinking agent compositions.
The use of Sn—O—SO2R-containing compounds, which can be prepared, for example, from alkyltin oxides and sulfonic acids, in, inter alia, condensation-crosslinking polymer systems is described. In this context, reference may be made, for example, to U.S. Pat. No. 3,095,434 and U.S. Pat. No. 5,981,685. The use of the claimed catalysts with Sn sulfonate units for RTV silicone systems is not described in the examples. Especially, alkoxy-RTV-1 systems with their specific problems regarding the shelf life and the necessity of cocatalyzing additives are not described.
EP-A 623 642 describes the addition of acids, including sulfonic acids, for stabilizing RTV-1 acetoxy materials if the polymers contained therein have been prepared by anionic polymerization of cyclic structures and, for example, phosphoric acid was used for neutralizing the basic polymerization catalysts and the materials therefore contain, for example, alkali metal phosphates.
The use of reaction products of sulfonic acids with amines or basic fillers is known in filled RTV systems, in order to facilitate the dispersing of the fillers and to obtain an elastomer having a low modulus. In this context, reference may be made, for example, to U.S. Pat. No. 5,073,586 and U.S. Pat. No. 5,118,738.